Liquid crystal optical modulation element and optical head device

ABSTRACT

To provide a liquid crystal optical modulation element which is excellent in durability against blue laser and which can maintain the characteristics for a long period of time. 
     A liquid crystal optical modulation element to modulate a laser beam having a wavelength of at most 500 nm, which comprises a layer of a polymer liquid crystal composition sandwiched between a pair of transparent substrates facing each other, characterized in that
         each of the pair of transparent substrates has an alignment film on the surface which faces the other transparent substrate, and   the polymer liquid crystal composition is a polymer liquid crystal containing a hindered amine compound and a hindered phenol compound.

TECHNICAL FIELD

The present invention relates to a liquid crystal optical modulationelement to be used for modulating a laser beam having a wavelength of atmost 500 nm, and an optical head device.

BACKGROUND ART

An optical element (such as a phase plate or a deflection element suchas a diffraction grating) employing liquid crystal is small in size andhas high durability since it has no mechanical moving portion, and thushas attracted attention as an optical modulation element, and as mountedon an optical head device, it is performing a role to modulate (e.g.deflect or diffract) a laser beam at the time of writing information onan optical disk or reading information from an optical disk.

For example, at the time of reading information, linearly-polarizedlight emitted from a laser light source is transmitted through adeflecting element and then through a ¼ phase plate and arrives at thesurface of an optical disk. The polarization direction of the outwardlinearly-polarized light is aligned in a direction not changed by thedeflecting element, and the outward linearly-polarized light is linearlytransmitted through the deflecting element and transformed by the ¼phase plate into a circularly-polarized light. This circularly-polarizedlight is reflected on the recording surface and becomes a reversedcircularly-polarized light, which is again transformed by the ¼ phaseplate into a linearly-polarized light perpendicular to incident light.Such a returning light beam will have its traveling direction bent whenit is again passed through the deflecting element, and arrives at alight receiving element.

Further, during reading or writing of information, if the optical diskundergoes plane wobbling or the like, the focus position of the beamspot will be displaced from the recording surface, and a servo mechanismwill be required to detect and correct the displacement to let the beamspot follow a concavo-convex pit on the recording surface. Such a servosystem for an optical disk is constructed so that the focus of a beamspot irradiated from a laser light source is adjusted on the recordingsurface, and then the track position is detected to let the beam spotfollow the desired track. Further, it is also necessary to make surethat the laser beam reflected without hitting the pit on the recordingsurface will not return as it is to the light source. Such opticalelements are not limited to optical pickup elements used for readingrecords on optical disks, but they are utilized also for imagingelements in application to projectors, etc. or communication devices inapplication to wavelength-tunable filters, etc.

In recent years, in order to increase the capacity of optical disks, ithas been attempted to shorten the wavelength of a laser beam to be usedfor writing or reading of information and to further reduce theconcavo-convex pit size on optical disks. At present, a laser beamhaving a wavelength of 780 nm is used for CD, and a laser beam having awavelength of 660 nm is used for DVD. For optical recording media ofnext generation, use of a laser beam having a wavelength of from 300 to450 nm is being studied. Accordingly, a liquid crystal element isdesired which modulates a laser beam having a wavelength of from 300 to450 nm (hereinafter referred to also as a blue laser beam).

As a material to obtain an optical element employing liquid crystal(hereinafter referred to also as a liquid crystal element), a polymerliquid crystal obtained by polymerizing a liquid crystal compositioncontaining a compound represented by the following formula (1) (whereinQ is a 1,4-phenylene group or a trans-1,4-cyclohexylene group, and Z isan alkyl group) has, for example, been reported (Patent Document 1).

However, conventional materials such as polymer liquid crystalsdisclosed in Patent document 1 have had a problem that the durabilityagainst a blue laser beam is inadequate. Therefore, the presentinventors have developed various polymerizable liquid crystal compounds(Patent Document 2) as materials having good durability against a bluelaser beam. Further, e.g. PCT/JP2005/001839 and Japanese PatentApplication No. 2005-301138 report on polymerizable liquid crystalcompounds having good durability against a blue laser beam.

The polymerizable liquid crystal compounds disclosed in e.g. PatentDocument 2, PCT/JP2005/001839 and Japanese Patent Application No.2005-301138 are compounds which satisfy the properties required for thematerials to be used for optical elements (such as a large value ofrefractive index anisotropy, low absorption of a laser beam andwavelength dispersion of refractive index) and which at the same timehave good durability against a blue laser beam.

Further, an element employing a polymer liquid crystal is prepared via apolymerization step such as polymerization after injecting apolymerizable liquid crystal into a cell, or polymerization afterapplying a polymerizable liquid crystal on a substrate. Suchpolymerization is usually carried out by photopolymerization. In a casewhere a polymerizable liquid crystal is injected into a cell or it isapplied on a substrate, it is necessary to heat the polymerizable liquidcrystal, and in order to prevent thermal polymerization, it is common toadd a polymerization inhibitor to the polymerizable liquid crystal.Particularly, injection of the polymerizable liquid crystal into a cellis usually carried out by injection under reduced pressure. Accordingly,the polymerization inhibitor is required to have a high boiling point inaddition to a high polymerization inhibiting ability. As such apolymerization inhibitor, 2-n-dodecylphenol is, for example, used.

On the other hand, a liquid crystalline material mixture containing anadditive selected from the group consisting of a light stabilizer, aheat stabilizer and/or an antioxidant, added to a liquid crystallinemixture, has been reported (Patent Document 3). Patent Document 3discloses that a 2,2,6,6-tetramethylpyperidine derivative or analkylated monophenol such as 2,6-di-t-butyl-4-methylphenol may be usedas the component of the light stabilizer, the heat stabilizer and/or theantioxidant.

Patent Document 1: JP-A-10-195138

Patent Document 2: WO2005/014522

Patent Document 3: JP-A-2002-536529

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

However, even in a case where the materials disclosed in e.g. PatentDocument 2, PCT/JP2005/001839 and Japanese Patent Application No.2005-301138 are used, there has been cases where the optical modulationproperties tended to deteriorate depending upon the conditions of use.Under the circumstances, the present inventors have conducted a study onincorporating a hindered amine compound to a polymerizable liquidcrystal disclosed in the above references in order to improve thestability against a blue laser beam. However, as a result of an exposuretest to a blue laser beam, it has been found that the durabilitysometimes deteriorates when a hindered amine compound is incorporated.

Means to Solve the Problems

The present invention has been made to solve the above problems and hasan object to provide a liquid crystal optical modulation element whichis capable of improving the durability against a blue laser beam with anelement employing a polymer liquid crystal and which is thereby capableof modulating a blue laser beam constantly over a long period of time.Namely, the present invention provides the following:

(1) A liquid crystal optical modulation element to modulate a laser beamhaving a wavelength of at most 500 nm, which comprises a layer of, apolymer liquid crystal composition sandwiched between a pair oftransparent substrates facing each other, characterized in that

each of the pair of transparent substrates has an alignment film on thesurface which faces the other transparent substrate, and

the polymer liquid crystal composition is a polymer liquid crystalcontaining a hindered amine compound and a hindered phenol compound.

(2) The liquid crystal optical modulation element according to the above(1), wherein the polymer liquid crystal composition is one obtainable bypolymerizing a polymerizable liquid crystal composition comprising apolymerizable liquid crystal, a hindered amine compound and a hinderedphenol compound.

(3) The liquid crystal optical modulation element according to the above(2), wherein the content of the hindered amine compound is from 0.05 to5 mass% based on the polymerizable liquid crystal.

(4) The liquid crystal optical modulation element according to above (2)or (3), wherein the content of the hindered phenol compound is from 0.05to 10 mass% based on the polymerizable liquid crystal.

(5) The liquid crystal optical modulation element according to any oneof the above (2) to (4), wherein the polymerizable liquid crystalcontains at least one of the following compounds (2) and (3):

CH₂═CR¹—COO—(L¹)_(k1)-E¹-E²-E³-(E⁴)_(m)-(E⁵)_(n)-R²   (2)

CH₂═CR³—COO—(L²)_(k2)-G¹-G²-G³-G⁴-R⁴   (3)

wherein each of R¹ and R³ is a hydrogen atom or a methyl group; R² is aC₁₋₈ alkyl group; R⁴ is a C₁₋₈ alkyl group or a fluorine atom; L¹ is—(CH₂)_(p1)O—, —(CH₂)_(q1)-, -Cy-COO—, -Cy-OCO—, -E⁶-(CH₂)₂—, -E⁷ -CH₂O—or -E⁸-O— (wherein Cy is a trans-1,4-cyclohexylene group, each of p1 andq1 which are independent of each other, is an integer of from 2 to 8);L² is —(CH₂)_(p2)O— or —(CH₂)_(q2)— (wherein each of p2 and q2 which areindependent of each other, is an integer of from 2 to 8); each of E¹,E², E³, E⁴, E⁵, E⁶, E⁷ and E⁸ which are independent of one another, is a1,4-phenylene group or a trans-1,4-cyclohexylene group (provided that atleast one of E¹, E² and E³ is a trans-1,4-cyclohexylene group, and in acase where L¹ is -Cy-OCO—, E¹ is a trans-1,4-cyclohexylene group); G¹ isa 1,4-phenylene group, each of G², G³ and G⁴ which are independent ofone another is a 1,4-phenylene group or a trans-1,4-cyclohexylene group,and at least one of G² and G³ is a trans-1,4-cyclohexylene group(provided that the 1,4-phenylene group and trans-1,4-cyclohexylene groupin G¹ to G⁴ may be such that a hydrogen atom bonded to a carbon atom ineach group may be substituted by a fluorine atom, a chlorine atom or amethyl group); and each of k1, k2, m and n which are independent of oneanother, is 0 or 1, provided that when k1 is 1 and L¹ is -Cy-COO—,-Cy-OCO—, -E⁶-(CH₂)₂—, -E⁷-CH₂O— or -E⁸-O—, at least one of m and n is0.

(6) The liquid crystal optical modulation element according to any oneof the above (1) to (5), which is used for a laser beam having awavelength of from 300 to 450 nm.

(7) An optical head device comprising a light source for emitting alaser beam having a wavelength of at most 500 nm, an objective lens forconverging the laser beam emitted from the light source on an opticalrecording medium, a photodetector for receiving the light converged andreflected on the optical recording medium, and the liquid crystaloptical modulation element as defined in any one of the above (1) to(6), disposed in an optical path between the light source and theoptical recording medium or in an optical path between the opticalrecording medium and the photodetector.

EFFECTS OF THE INVENTION

According to the present invention, the optical modulationcharacteristics of a liquid crystal optical modulation element tomodulate a blue laser beam can be well maintained.

BEST MODE FOR CARRYING OUT THE INVENTION

In this specification, a compound represented by the formula (1) will bereferred to also as a compound (1). A group represented by the formula(A) will be referred to also as a group (A). The same applies to othercompounds and groups. Further, the wavelength is meant to cover therange of the disclosed value ±2 nm even when it is disclosed by onepoint value. Further, “Ph” represents a 1,4-phenylene group, and “Cy”represents a trans-1,4-cyclohexylene group. A hydrogen atom in eachgroup of Ph and Cy may be substituted by a fluorine atom, a chlorineatom or a methyl group.

The liquid crystal optical modulation element of the present inventionis a liquid crystal optical modulation element to modulate a laser beamhaving a wavelength of at most 500 nm, which comprises a layer of apolymer liquid crystal composition sandwiched between a pair oftransparent substrates facing each other, wherein each of the pair oftransparent substrates has an alignment film on the surface which facesthe other transparent substrate, and the polymer liquid crystalcomposition is a polymer liquid crystal containing a hindered aminecompound and a hindered phenol compound.

As a method for sandwiching the polymer liquid crystal composition(hereinafter described in detail) between a pair of transparentsubstrates facing each other, the following methods may be mentioned,and preferred is method 1.

Method 1: A method wherein a cell is prepared by using a pair oftransparent substrates, and a polymerizable liquid crystal compositiondescribed hereinafter, is injected into the cell, followed bypolymerization.

Method 2: A method wherein a polymerizable liquid crystal composition isapplied on a surface of one transparent substrate having an alignmentfilm formed thereon, and then polymerized to form a polymer liquidcrystal composition, and then a polymerizable liquid crystal compositionis supplied, and another substrate provided with an alignment film islaminated, followed by polymerization.

Now, method 1 will be described in detail. The cell is assembled andprepared by disposing a pair of laminates each comprising a transparentsubstrate and an alignment film, so that the alignment film sides willface each other, and sealing the peripheral portion of the laminateswith a sealing agent. The laminate is preferably a laminate formed byapplying and drying a material for an alignment film on the surface of atransparent substrate, or a laminate formed by vapor-depositing amaterial for an alignment film on the surface of a transparentsubstrate.

The transparent substrate is preferably a transparent glass substrate ora transparent resin substrate, particularly preferably a transparentglass substrate as the rigidity is high. The thickness of thetransparent substrate is preferably from 0.2 to 1.5 mm, particularlypreferably from 0.3 to 1.1 mm. As the alignment film, an alignment filmmade of an organic substance such as a polyimide or an alignment filmmade of an inorganic material may be used. The alignment film made of anorganic substance such as a polyimide is preferably such that thesurface is subjected to rubbing treatment.

Preparation of the cell may be carried out by a usual method. Forexample, it may be prepared by the following method. Firstly, a pair ofthe above-mentioned laminates are prepared, and along the peripheralportion of the side of at least one of the laminates, on which analignment film is formed, a sealing agent such as an epoxy resin isapplied in a ring shape. To the sealing agent, spacers to obtain adesired cell gap, may preliminarily be incorporated. Then, the pair oflaminates are disposed with a space (a cell gap) so that the alignmentfilm sides face each other, and the sealing agent is cured to form anempty cell. The ring-shaped coated portion of the sealing agent isprovided at least partially with a non-continuous portion which will bean injection inlet for a liquid crystal composition to be injected.Here, the cell gap is preferably from 1 to 10 μm, particularlypreferably from 2 to 8 μm.

The construction of the liquid crystal optical modulation element is notlimited to the above construction. For example, a reflection preventivefilm may be laminated on the side opposite to the side of thetransparent substrate on which an alignment film is laminated, or aphase plate or the like may be laminated.

The polymer liquid crystal composition in the present invention is acomposition such that a polymer liquid crystal contains a hindered aminecompound and a hindered phenol compound. Such a polymer liquid crystalcomposition is preferably one obtainable by polymerizing a polymerizableliquid crystal composition comprising a polymerizable liquid crystal, ahindered amine compound and a hindered phenol compound.

The polymerizable liquid crystal is not particularly limited, but it maybe a polymerizable liquid crystalline compound having one or twopolymerizable functional groups and a mesogen structure, or apolymerizable liquid crystalline mixture having two or more suchpolymerizable liquid crystalline compounds mixed.

The polymerizable functional group is preferably an acryloyl group or amethacryloyl group, particularly preferably an acryloyl group. Further,the number of polymerizable functional groups is preferably one.

The mesogen structure preferably has the following structure, wherebythe durability against a blue laser beam is good, and the value of therefractive index anisotropy (Δn) can be made large.

(a) It contains a trans-1,4-cyclohexylene group and a 1,4-phenylenegroup as cyclic groups, and the total number of such cyclic groups isfrom 3 to 5.

(b) Among such cyclic groups, at least one is a trans-1,4-cyclohexylenegroup, and at least two are 1,4-phenylene groups.

(c) In a case where at least three 1,4-phenylene groups are contained,the number of 1,4-phenylene groups directly bonded or continuouslybonded via a connecting group having an unsaturated bond, is up to two.Accordingly, a trans-1,4-cyclohexylene group is interposed between1,4-phenylene groups not to let three or more 1,4-phenylene groups becontinuous.

(d) It contains no Ph—CO— structure.

Such a polymerizable liquid crystalline compound may, for example, be acompound represented by the following formula (2) (seePCT/JP2005/001839), a compound represented by the following formula (3)(see Japanese Patent Application No. 2005-301138) or a compoundrepresented by the following formula (4) (see Patent Document 2).Preferred is the compound (2) or the compound (3).

CH₂═CR¹—COO-(L¹)_(k1)-E¹-E²-E³-(E⁴)_(m)-(E⁵)_(n)-R²   (2)

CH₂═CR³—COO-(L²)_(k2)-G¹-G²-G³-G⁴-R⁴   (3)

Firstly, the compound (2) will be described. The symbols in the formula(2) have the following meanings.

R¹: A hydrogen atom or a methyl group.

R²: A C₁₋₈ alkyl group.

L¹: —(CH₂)_(p1)O—, —(CH₂)_(q1)—, -Cy-COO—, -Cy-OCO—, -E⁶-(CH₂)₂—,-E⁷-CH₂O—, or -E⁸-O— (wherein each of p1 and q1 which are independent ofeach other, is an integer of from 2 to 8).

E¹, E², E³, E⁴, E⁵, E⁶, E⁷, E⁸: Each independently a 1,4-phenylene groupor a trans-1,4-cyclohexylene group (provided that at least one of E¹, E²and E³ is a trans-1,4-cyclohexylene group, and in a case where L1 is-Cy-OCO—, E¹ is a trans-1,4-cyclohexylene group).

k1, m, n: Each independently 0 or 1, provided that when k1 is 1 and L¹is -Cy-COO—, -Cy-OCO—, -E⁶-(CH₂)₂—, -E⁷-CH₂O— or -E⁸-O—, at least one ofm and n is 0.

R¹ is preferably a hydrogen atom. When R¹ is a hydrogen atom,polymerization of the polymerizable liquid crystal composition readilyproceeds, such being preferred. Further, there is an advantage such thatthe characteristics of the obtainable polymer liquid crystal compositionare hardly susceptible to an influence of the external environment (suchas the temperature), and the in-plane distribution of the retardation issmall.

R² is a C₁₋₈ alkyl group, whereby T_(m) (the crystal phase-nematic phasetransition point) of the polymerizable liquid crystal composition can bemade low. R² is preferably a C₂₋₆ alkyl group. Further, R² is preferablylinear, since it is thereby possible to broaden the temperature rangewherein the compound (2) shows liquid crystallinity.

L¹ is —(CH₂)_(p1)O—, —(CH₂)_(q1)—, -Cy-COO—, -Cy-OCO—, -E⁶-(CH₂)₂—,-E⁷-CH₂O— or -E⁸-O— (wherein each of p1 and q1 which are independent ofeach other, is an integer of from 2 to 8, preferably an integer of from4 to 6, and each of E⁶, E⁷ and E⁸ is a 1,4-phenylene group or atrans-1,4-cyclohexylene group, preferably a non-substituted group).

L¹ is preferably -Cy-COO—, -Cy-OCO—, —(CH₂)_(p1)O— (preferably—(CH₂)₆O—) or —Ph—(CH₂)₂O—.

In a case where L¹ is -Cy-COO—, Δn of the polymer liquid crystalcomposition obtainable by the polymerization, can be made large. L¹ ispreferably -Cy-OCO— from such a viewpoint that the compatibility withanother polymerizable liquid crystal is good, and T_(m) can be made low.

Further, in general, when the polymerizable liquid crystal ispolymerized, the value of Δn tends to decrease between before and afterthe polymerization reaction. However, when L¹ is a group having apolymethylene group such as —(CH₂)_(p1)O— or —(CH₂)_(q1)—, the decreasein the Δn value between before and after the polymerization reaction canbe suppressed.

Each of k1, m and n which are independent of one another, is 0 or 1,provided that when k1 is 1 and L¹ is -Cy-COO—, -Cy-OCO—, -E⁶-(CH₂)₂—,-E⁷-CH₂O— or -E⁸-O—, at least one of m and n is 0.

Each of E¹, E², E³, E⁴ and E⁵ which are independent of one another, is a1,4-phenylene group or a trans-1,4-cyclohexylene group. The number ofcyclic groups which the compound (2) has, is from 3 to 5, provided thatat least one of E¹, E² and E³ is Cy, and in a case where L¹ is -Cy-OCO—,E¹ is a trans-1,4-cyclohexylene group. Further, at least one of E¹, E²and E³ is preferably Ph.

Further, in a case where a plurality of Ph are contained, the number ofPh connected by direct bonding is preferably 2.

The structure of “E¹-E²-E³” is preferably “Cy-Ph-Ph”, whereby Δn of thecompound (2) can be made large. It is thereby made easy to prepare aliquid crystal composition showing a larger Δn. Further, from such aviewpoint that absorption of a blue laser beam can be suppressed,“Cy-Ph-Cy” is preferred.

The compound (2) is preferably the following compound (2A) or thefollowing compound (2B) (Ph and Cy in the examples of the compound (2)are preferably non-substituted groups, respectively.)

CH₂═CR¹—COO-L¹-E¹-E²-E³-R²   (2A)

CH₂═CR¹—COO-E¹-E²-E³-R²   (2B)

As the compound (2A), the following compounds are preferred.

CH₂═CR¹—COO-Cy-COO-E¹-E²-E³-R²   (2Aa)

CH₂═CR¹—COO-Cy-OCO-E¹-E²-E³-R²   (2Ab)

CH₂═CR¹—COO-Ph-(CH₂)₂-E¹-E²-E³-R²   (2Ac)

CH₂═CR¹—COO-Ph-(CH₂)₂-E¹-E²-E³-R²   (2Ad)

Specifically, the following compounds are preferred, provided that arepresents an integer of from 1 to 8.

CH₂═CR¹—COO-Cy-COO-Cy-Ph-Ph-(CH₂)_(a)H   (2Aa1)

CH₂═CR¹—COO-Cy-COO-Cy-Ph-Cy-(CH₂)_(a)H   (2Aa2)

CH₂═CR¹—COO-Cy-OCO-Cy-Ph-Ph-(CH₂)_(a)H   (2Ab1)

CH₂═CR¹—COO-Cy-OCO-Cy-Ph-Cy-(CH₂)_(a)H   (2Ab2)

CH₂═CR¹—COO—(CH₂)_(p1)O-Ph-Cy-Ph-(CH₂)_(a)H   (2Ac1)

CH₂═CR¹—COO-Ph-(CH₂)₂-Ph-Ph-Cy-(CH₂)_(a)H   (2Ad1)

Among them, the compounds wherein R¹ is a hydrogen atom are preferred,and the compounds wherein a is from 2 to 6 are particularly preferred.Further, with respect to the compound (2Ac1), the compound wherein p1 isfrom 4 to 6 is preferred, and the compound wherein p1 is 6, isparticularly preferred.

The compound (2B) is preferably the following compound (2Ba) or thefollowing compound (2Bb).

CH₂═CR¹—COO-Ph-Cy-Ph-R²   (2Ba)

CH₂═CR¹—COO-Ph-Ph-Cy-R²   (2Bb)

Specifically, the following compounds are preferred, provided that arepresents an integer of from 1 to 8. Among them, the compounds whereinR¹ is a hydrogen atom, and a is from 2 to 6, are particularly preferred.

CH₂═CR¹—COO-Ph-Cy-Ph-(CH₂)_(a)H   (2Ba1)

CH₂═CR—COO-Ph-Ph-Cy-(CH₂)_(a)H   (2Bb1)

Now, the compound (3) will be described. The symbols in the formula (3)have the following meanings.

CH₂═CR³—COO-(L²)_(k2)-G¹-G²-G³-G⁴-R⁴   (3)

R³: A hydrogen atom or a methyl group.

R⁴: A C₁₋₈ alkyl group or a fluorine atom.

k2: 0 or 1.

L²: —(CH₂)_(p2)O— or —(CH₂)_(q2)— (wherein each of p2 and q2 which areindependent of each other, is an integer of from 2 to 8).

G¹: A 1,4-phenylene group.

G², G³, G⁴: Each independently a 1,4-phenylene group or atrans-1,4-cyclohexylene group, and at least one of G² and G³ is atrans-1,4-cyclohexylene group.

However, the 1,4-phenylene group and the trans-1,4-cyclohexylene groupin G¹, G², G³ and G⁴ may be such that a hydrogen atom bonded to a carbonatom in such a group may be substituted by a fluorine atom, a chlorineatom or a methyl group.

Preferred embodiments of R³ are the same as those of R¹.

R⁴ is a C₁₋₈ alkyl group or a fluorine atom, whereby the melting point(T_(m)) (namely, the crystal phase-nematic phase transition point) ofthe polymerizable liquid crystal composition containing the compound (3)can be made low. R⁴ is more preferably a C₂₋₆ alkyl group or a fluorineatom. Further, when R⁴ is an alkyl group, it is preferably of a linearstructure, whereby the temperature range wherein the compound (3) showsliquid crystallinity, can be broadened.

k2 is 0 or 1, and preferably 1 in the present invention.

L² is —(CH₂)_(p2)O— or —(CH₂)_(q2)—, preferably —(CH₂)_(p2)O—.

Also in the case of the compound (3), when L² is a group having apolymethylene group such as —(CH₂)_(p2)O— or —(CH₂)_(q2)—, the decreasein the Δn value between before and after the polymerization can besuppressed.

G¹ is a 1,4-phenylene group, and each of G², G³ and G⁴ which areindependent of one another, is a 1,4-phenylene group or atrans-1,4-cyclohexylene group. The number of cyclic groups which thecompound (3) has, is 4, and at least one of G² and G³ is Cy. Further, atleast one of G², G³ and G⁴ is preferably Ph. Further, in a case where aplurality of Ph are contained, two Ph are preferably adjacent to eachother, whereby the value of Δn can be made large. However, if three ormore Ph are directly bonded, the durability against a blue laser maydeteriorate. In the compound (3) , when at least one of G² and G³ is Cy,there is no possibility that three or more Ph are directly bonded oneanother.

The structure of “G¹-G²-G³-G⁴” may be “Ph-Ph-Cy-Ph”, “Ph-Cy-Ph-Ph”,“Ph-Ph-Cy-Cy”, “Ph-Cy-Cy-Ph”, “Ph-Cy-Ph-Cy” or “Ph-Cy-Cy-Cy”. Amongthem, “Ph-Cy-Ph-Ph”, “Ph-Ph-Cy-Cy” and “Ph-Ph-Cy-Ph” are preferred,since Δn of the compound (1) can be made large. It is thereby made easyto prepare a polymerizable liquid crystal composition showing a largerΔn. As the compound (3), the following compounds (3A) to (3C) arepreferred.

CH₂═CR³—COO-L²-Ph-Ph-Cy-Cy-R⁴   (3A)

CH₂═CR³—COO-L²-Ph-Cy-Ph-Ph-R⁴   (3B)

CH₂═CR³—COO-L²-Ph-Ph-Cy-Ph-R⁴   (3C)

Among them, the compounds wherein R³ is a hydrogen atom, and R⁴ is aC₂₋₆ linear alkyl group or a fluorine atom, are preferred, and thecompounds wherein -L²- is —(CH₂)_(p2)O— (p2 is particularly preferablyan integer of from 4 to 6) are particularly preferred.

Further, the 1,4-phenylene group and the trans-1,4-cyclohexylene groupin G¹, G², G³ and G⁴ may be such that a hydrogen atom bonded to a carbonatom in such a group may be substituted by a fluorine atom, a chlorineatom or a methyl group. In the present invention, the 1,4-phenylenegroup is preferably a non-substituted group, a group substituted by onefluorine atom, or a group substituted by one methyl group. In a casewhere the 1,4-phenylene group has such a substituent, there may beeffects to lower the melting point and to lower the viscosity of thecompound (3). Further, the position of such a substituent is preferablyat the 2- or 3-position. Further, the trans-1,4-cyclohexylene group ispreferably a non-substituted group.

As the compound (3), the following compounds are preferred, and thecompounds (3A-1), (3A-3), (3A-5), (3B-1), (3B-3), (3B-4), (3B-5), (3C-1)and (3C-2) are particularly preferred. In the formulae, p2 is as definedabove and is preferably an integer of from 4 to 6. R⁴¹ is a C₁₋₈ alkylgroup, preferably a C₂₋₆ linear alkyl group.

Now, the compound (4) will be described. The symbols in the formula (4)have the following meanings.

R⁵: A hydrogen atom or a methyl group.

R⁶: A C₁₋₈ alkyl group.

Cy: A trans-1,4-cyclohexylene group.

X¹: A 1,4-phenylene group or a trans-1,4-cyclohexylene group.

However, the above 1,4-phenylene group and trans-1,4-cyclohexylene groupmay be such that a hydrogen atom in such a group may be substituted by afluorine atom, a chlorine atom or a methyl group.

Preferred embodiments of R⁵ are the same as those of R¹, and preferredembodiments of R⁶ are the same as those of R².

X¹ is a 1,4-phenylene group or a trans-1,4-cyclohexylene group. In acase where X¹ is a 1,4-phenylene group, among three cyclic groupscontained in the compound (4), two will be 1,4-phenylene groups.Accordingly, as compared with a compound wherein all of the three cyclicgroups are 1,4-phenylene groups, it is stable against a blue laser beam,and as compared with a compound having only one 1,4-phenylene group, theoptical anisotropy such as the refractive index anisotropy will belarge. Accordingly, it will be easy to obtain the desired opticalanisotropy even when a liquid crystal composition for a diffractionelement requiring a particularly large retardation value is to beprepared. Further, the degree of freedom in preparation of the liquidcrystal composition will be broadened. When X¹ is atrans-1,4-cyclohexylene group, the stability of the compound (4) againsta blue laser beam, can further be improved, and the nematicphase-isotropic phase transition point can be made high.

In the compound (4), the 1,4-phenylene group and thetrans-1,4-cyclohexylene group may be non-substituted groups, or ahydrogen atom bonded to a carbon atom in such a group may be substitutedby a fluorine atom, a chlorine atom or a methyl group. A non-substitutedgroup is preferred from such a viewpoint that the nematicphase-isotropic phase transition point of the compound (4) can be madehigh.

As specific examples of the compound (4), the following compounds may bementioned, provided that b is an integer of from 1 to 8. Among thefollowing compounds, a compound wherein R⁵ is a hydrogen atom, and b isfrom 2 to 6, is particularly preferred (Ph and Cy in examples of thecompound (4) are preferably non-substituted groups, respectively.)

CH₂═CR⁵—COO-Ph-OCO-Cy-Ph-(CH₂)_(b)H   (4A)

CH₂═CR⁵—COO-Ph-OCO-Cy-Cy-(CH₂)_(b)H   (4B)

Among the compounds (2) to (4), the following polymerizable liquidcrystalline compounds are preferred.

Further, solely with the polymerizable liquid crystalline compoundshaving at least three cyclic groups such as the above compounds (2) to(4), there may be a case where the crystal phase-nematic phasetransition point of the polymerizable liquid crystal composition tendsto be high, and the operation efficiency tends to deteriorate. In such acase, it is preferred to use another polymerizable liquid crystallinecompound in combination with the above compounds (2) to (4). As suchanother polymerizable liquid crystal compound, the following compound(5) is preferred.

CH₂═CR⁷—COO—(N)_(r)-W⁸-W⁹-R⁸   (5)

The symbols in the formula have the following meanings.

R⁷: A hydrogen atom or a methyl group.

R⁸: A C₁₋₈ alkyl group.

r: 0 or 1.

N: —(CH₂)_(s)O— or —(CH₂)_(t)— (wherein each of s and t which areindependent of each other, is an integer of from 2 to 8).

W⁸, W⁹: Each independently a 1,4-phenylene group or atrans-1,4-cyclohexylene group, provided that the above 1,4-phenylenegroup and trans-1,4-cyclohexylene group are such that a hydrogen atombonded to a carbon atom in such a group may be substituted by a fluorineatom, a chlorine atom or a methyl group.

Specifically, the following compounds (5A) to (5D) are preferred, andthe following compound (5A) is particularly preferred, provided that cis an integer of from 1 to 8, preferably from 2 to 6.

CH₂═CR⁷—COO-Cy-Cy-(CH₂)_(c)H   (5A)

CH₂═CR⁷—COO-Cy-Ph-(CH₂)_(c)H   (5B)

CH₂═CR⁷—COO-Ph-Cy-(CH₂)_(c)H   (5C)

CH₂═CR⁷—COO-Ph-Ph-(CH₂)_(c)H   (5D)

Specifically, the following compound (5A-1) is preferred.

The polymerizable liquid crystal is preferably a mixture comprising atleast one compound (2) and at least one compound (3), or a mixturecomprising at least one compound selected from the compound (2) and thecompound (3) and at least one compound (5).

In the former, the amount of the compound (2) is preferably from 30 to70 mol %, particularly preferably from 40 to 60 mol %, based on thetotal polymerizable liquid crystal. The amount of the compound (3) ispreferably from 30 to 70 mol %, particularly preferably from 40 to 60mol %, based on the total polymerizable liquid crystal.

In the latter, the total amount of the compound (2) and the compound (3)is preferably from 5 to 90 mol %, particularly preferably from 10 to 60mol %, based on the total polymerizable liquid crystal. The amount ofother polymerizable liquid crystal such as the compound (5) ispreferably from 10 to 95 mol %, particularly preferably from 40 to 90mol %, based on the total polymerizable liquid crystal.

As the polymerizable liquid crystal, the following polymerizable liquidcrystalline mixtures are preferred.

A polymerizable liquid crystalline mixture comprising the compound(2Bb1-1) and the compound (5A-1).

A polymerizable liquid crystalline mixture comprising the compound(2Ab1-1) and the compound (5A-1).

A polymerizable liquid crystalline mixture comprising the compound(3B-1-1) and the compound (2Ba1-1).

As the hindered amine compound in the present invention, a compoundhaving at least one group represented by the following formula (A) ispreferred, and a 2,2,6,6-tetraalkylpyperidine derivative is particularlypreferred. Here, hindered amine compounds may be used alone or incombination as a mixture of two or more of them.

In the formula, each of R⁹, R¹⁰, R¹¹ and R¹² is an alkyl group or aphenyl group, and R¹³ is a hydrogen atom, an alkyl group or an alkoxygroup.

As R⁹, R¹⁰, R¹¹ and R¹², an alkyl group is preferred. Such a group maybe of a linear structure or a branched structure, preferably of a linearstructure. As R⁹, R¹⁰, R¹¹ and R¹², an ethyl group or a methyl group ispreferred, and a methyl group is particularly preferred. R⁹, R¹⁰, R¹¹and R¹² may be the same groups or different groups, preferably the samegroups. It is particularly preferred that all of R⁹, R¹⁰, R¹¹ and R¹²are methyl groups.

In a case where R¹³ is an alkyl group, it is preferably a C₁₋₄ linearalkyl group, particularly preferably a methyl group. In a case where R¹³is an alkoxy group, such an alkoxy group may be of a linear structure, abranched structure or of a structure having partially a ring, preferablyof a linear structure. The number of carbon atoms constituting such analkoxy group is from 1 to 18, preferably from 1 to 10. Such an alkoxygroup may, for example, be a n-octyloxy group, a n-propyloxy group or an-hexyloxy group, and a n-octyloxy group is preferred. R¹³ is preferablya hydrogen atom, a methyl group or a n-octyloxy group, and a methylgroup is particularly preferred since the stabilizing effect against ablue laser beam is high.

As the group represented by the formula (A), the following group (A1),the following group (A2) or the following group (A3) is preferred.

As the hindered amine compound in the present invention, the followingcompounds may, for example, be mentioned, and a compound having at leasttwo 2,2,6,6-tetraalkylpyperidine rings, is preferred.

The hindered phenol compound in the present invention is a compoundhaving substituents at both the 2- and 6-positions to the phenolichydroxyl group. As such substituents, a methyl group or a t-butyl groupis preferred, and a t-butyl group is particularly preferred. Thecombination of the substituents and the substituted positions may, forexample, be as follows:

(i) a case where the 2-position is substituted by a methyl group, andthe 6-position is substituted by a t-butyl group,

(ii) a case where the 2-position is substituted by a t-butyl group, andthe 6-position is substituted by a methyl group,

(iii) a case where both the 2- and 6-positions are substituted by methylgroups, and

(iv) a case where both the 2- and 6-position are substituted by t-butylgroups. The case (iv) is preferred.

The hindered phenol compound may be any one of monophenols, bisphenolsand polyphenols and may be suitably selected for use among compoundscommercially available as phenol type antioxidants. Such hindered phenolcompounds may be used alone or in combination as a mixture of two ormore of them.

As the hindered phenol compound, the following compounds may, forexample, be mentioned, and a compound having at least two phenols ispreferred.

The content of the hindered amine compound is preferably from 0.05 to 5mass%, particularly preferably from 0.1 to 1 mass %, based on thepolymerizable liquid crystal. When the content of the hindered aminecompound is from 0.05 to 5 mass %, the light resistance can be improvedwithout presenting an influence over the polymerization behavior of thepolymerizable liquid crystal composition.

Whereas, the content of the hindered phenol compound is preferably from0.05 to 10 mass %, particularly preferably from 0.1 to 5 mass %, basedon the polymerizable liquid crystal. When the content of the hinderedphenol compound is from 0.05 to 10 mass %, the light resistance can beimproved without presenting an influence over the polymerizationbehavior of the polymerizable liquid crystal composition. Further, thehindered phenol compound has a polymerization inhibiting ability.Accordingly, if its amount is too much, polymerization of thepolymerizable liquid crystal composition is likely not to proceed, andif its amount is too small, polymerization by e.g. heat is likely toproceed.

The ratio of the hindered amine compound to the hindered phenol compoundin the polymer liquid crystal composition is preferably from 0.1 to 50,particularly preferably from 0.5 to 30 by the mass ratio of hinderedamine compound/hindered phenol compound.

In the polymer liquid crystal composition obtained by polymerizing thepolymerizable liquid crystal composition containing the hindered aminecompound and the hindered phenol compound within the above ranges, thecontent of the hindered amine compound will be from about 0.05 to 5 mass%, based on the polymer liquid crystal, and the content of the hinderedphenol compound will be from about 0.05 to 10 mass %, based on thepolymer liquid crystal.

Further, in order to let the polymerization proceed smoothly, thepolymerizable liquid crystal composition preferably contains apolymerization initiator. The polymerization is carried out byphotopolymerization, and accordingly, the polymerization initiator issuitably selected from photopolymerization initiators such asacetophenones, benzophenones, benzoins, benzyls, Michler ketones,benzoin alkyl ethers, benzyl dimethyl ketals and thioxanthones. Withsuch a photopolymerization initiator, its residue will remain in thepolymer liquid crystal composition, and therefore, it preferably has alow absorption of a blue laser beam. As such a polymerization initiator,Irgacure 754 (manufactured by Ciba Specialty Chemicals K.K.) may, forexample, be mentioned. The amount of the polymerization initiator ispreferably from 0.1 to 5 mass %, particularly preferably from 0.3 to 2mass %, based on the entire amount of the polymerizable liquid crystal.

The polymerizable liquid crystal composition in the present inventionmay contain components (hereinafter referred to as other components)other than the polymerizable liquid crystal, the hindered aminecompound, the hindered phenol compound and the polymerization initiator.As such other components, a chiral compound, an ultraviolet absorber anda dichroic dye may, for example, be mentioned. Further, the hinderedphenol compound has a polymerization-inhibiting ability, andaccordingly, in the present invention, a polymerization inhibitor maynot necessarily be used, but in some cases, a polymerization inhibitormay be used.

The proportion of other components is preferably adjusted depending uponthe particular application. For example, when a chiral compound is to beused as other component, the amount of the chiral compound is preferablyfrom 5 to 80 mass %, particularly preferably from 5 to 50 mass %, basedon the polymer liquid crystal. Here, as the chiral compound, anon-polymerizable chiral compound or a polymerizable chiral compound maybe used.

When a dichroic dye is to be used as other component, the amount of thedichroic dye is preferably from 1 to 20 mass %, particularly preferablyfrom 3 to 18 mass %, based on the polymer liquid crystal.

When an ultraviolet absorber is to be used as other component, it ispreferably at most 5 mass %, particularly preferably at most 2 mass %,based on the polymer liquid crystal.

In the present invention, the above polymerizable liquid crystalcomposition is injected into a cell, followed by polymerization toobtain a polymer liquid crystal composition. The polymerization ispreferably carried out in a state where the polymerizable liquid crystalcomposition shows a liquid crystal phase and in a state where the liquidcrystal is aligned. In order to maintain the state where thepolymerizable liquid crystal composition shows a liquid crystal phase,the ambient temperature may be controlled to be at most the nematicphase-isotropic phase transition temperature (T_(c)). However, at atemperature close to T_(c), Δn of the polymerizable liquid crystalcomposition is very small, and accordingly, the upper limit of theambient temperature is preferably at most (T_(c)−10)° C. Further, thepolymerization is preferably carried out by photopolymerization.

The polymer liquid crystal composition prepared by the above process maybe used as it is sandwiched between transparent substrates or may beused as peeled from the transparent substrates and supported on anothersubstrate.

The liquid crystal optical modulation element of the present inventionmodulates a laser beam having a wavelength of at most 500 nm, preferablya laser beam having a wavelength of from 350 to 500 nm, particularlypreferably a laser beam having a wavelength of from 350 to 450 nm.Specifically, there is a case where the polarization state or thewavefront state of the blue laser beam which entered the liquid crystaloptical modulation element is modulated. Modulation of the polarizationstate may, for example, be a case where the entering linearly polarizedlight is modulated to an elliptically polarized light, a case where itis modulated to a circularly polarized light or a case where it ismodulated to a linearly polarized light at right angles to the incidentpolarized light, and a liquid crystal optical modulation element havingsuch a function can be utilized as a polarized light conversion element.The polarized light conversion element can be used as a light quantitycontrol element as combined with a polarization beam splitter or apolarizing plate. Further, the liquid crystal optical modulation elementto modulate the wavefront state can be utilized e.g. as an aberrationcorrection element. Specifically, an aberration correction element toprevent reading error or an aberration correction element to suppressaberration simultaneously at all the wavelengths in the multi-wavelengthcompatible optical head device which compatibly employs at least twodifferent wavelengths, may, for example, be mentioned. Further, it maybe used also as a diffraction element such as a diffraction grating.

Further, the above polarized light conversion element, light quantitycontrol element, aberration correction element and diffraction elementmay be applied not only to an optical head device but also to aprojector.

EXAMPLES

Now, the present invention will be described in detail with reference toExamples, but it should be understood that the present invention is byno means thereby restricted. Here, Examples 1 to 4, 7, 9 to 11, 14 and15 are Comparative Examples, and Examples 5, 6, 8, 12, 13 and 16 areWorking Examples of the present invention.

(1) Preparation of Cell (1-1) Preparation Example for Cell

On a glass substrate of 5 cm×5 cm×0.5 mm in thickness, a polyimidesolution was applied by a spin coater and dried, followed by rubbingtreatment in a prescribed direction by means of nylon cloth to prepare atransparent substrate. Two such substrates were bonded by means of anadhesive so that the surfaces having alignment treatment applied, facedeach other, thereby to prepare a cell. To the adhesive, glass beadshaving a diameter of 4 μm were added, and the distance between thesubstrates became 4 μm.

(2) Preparation of Polymerizable Liquid Crystal Composition

As the polymerizable liquid crystalline compound, the following compound(2Ab1-1), the following compound (2Bb1-1), the following compound(2Bb1-2), the following compound (2Ba1-1), the following compound(3B-1-1), the following compound (5A-1) and the following compound(5A-2) were used. As a hindered amine compound, the following compound(A2-3) (product No.: LA62, manufactured by Asahi Denka Kogyo K.K.) andthe following compound (A3-1) (product No.: TINUVIN123, manufactured byCiba Specialty Chemicals K.K.) were used. As the hindered phenolcompound, the following compound (B-1) (product No.: A060, manufacturedby Asahi Denka Kogyo K.K.) and the following compound (B-4) (product No.AO50, manufactured by Asahi Denka Kogyo K.K.) were used. As thepolymerization initiator, Irgacure 754 (manufactured by Ciba SpecialtyChemicals K.K.) was used. Further, 2-n-dodecylphenol (hereinafterreferred to simply as 2NDP, manufactured by Tokyo Kasei Kogyo Co., Ltd.)was used.

Compound (2Bb1-1) and compound (5A-2) were mixed in a molar ratio of28:72 to obtain polymerizable liquid crystal 1. Further, compound(2Bb1-1), compound (2Bb1-2), compound (5A-1) and compound (5A-2) weremixed in a molar ratio of 14:14:36:36 to obtain polymerizable liquidcrystal 2. Further, compound (2Ab1-1), compound (5A-1) and compound(5A-2) were mixed in a molar ratio of 50:25:25 to obtain polymerizableliquid crystal 3. Further, (2Ba1-1) and compound (3B1-1) were mixed in amolar ratio of 45:55 to obtain polymerizable liquid crystal 4.

Then, to these polymerizable liquid crystals 1 and 2, the hindered aminecompound, the hindered phenol compound and the polymerization initiatorwere mixed in the proportions shown in Tables 1 to 4 to preparepolymerizable liquid crystal compositions. Here, the hindered aminecompound, the hindered phenol compound and the polymerization initiatorare represented by mass % values, respectively, based on thepolymerizable liquid crystal. Further, the nematic phase-isotropic phasetransition point of the compositions using such polymerizable liquidcrystal 1 and polymerizable liquid crystal 2 was at least 125° C. ineach case. The nematic phase-isotropic phase transition point of thecompositions using polymerizable liquid crystal 3 was at least 200° C.and not measurable, since they underwent thermal polymerization.Further, the crystal phase-nematic phase transition point of thecompositions using polymerizable liquid crystal 3 was in the vicinity of100° C. in each case. Further, the nematic phase-isotropic phasetransition point of the compositions using polymerizable liquid crystal4 was at least 155° C. in each case.

Compound (2Bb1-1) was prepared as follows.

Preparation of Compound (2Bb1-1) Preparation Example for Compound (Q-1)

Into a 1 L four-necked flask equipped with a reflux condenser and astirrer, compound (N-1) (18.2 g, 0.064 mol), compound (P) (9.75 g, 0.064mol), Pd[P(C6H₅)₃]₄ (5.55 g, 0.0048 mol), a 20% sodium carbonate aqueoussolution (400 mL) and tetrahydrofuran (640 mL) were added, and in anitrogen stream, a reaction was carried out at 70° C. for 24 hours.After completion of the reaction, water and diethyl ether were added forliquid separation, and an organic layer was recovered. The recoveredorganic layer was washed with a saturated sodium chloride aqueoussolution (40 mL) and then washed with water, and an organic layer wasagain recovered. The organic layer was dried over anhydrous magnesiumsulfate and then subjected to filtration under reduced pressure toremove anhydrous magnesium sulfate. The filtrate was purified by columnchromatography (developer: dichloromethane/hexane=5/5 by volume ratio)to obtain a fraction containing the desired product. The fraction wasconcentrated to obtain powdery crystal. To this powdery crystal, asolvent mixture (90 mL) of dichloromethane and hexane was added, andrecrystallization was carried out to obtain compound (Q-1) (17.4 g). Theyield was 86%.

Preparation Example for Compound (R-1)

Into a 500 mL four-necked flask equipped with a reflux condenser, astirrer and a dropping apparatus, compound (Q-1) (10 g, 0.032 mol)obtained in the above Preparation Example and dichloromethane (300 mL)were added. In a nitrogen stream, a 1 mol/L borontribromide-dichlromethane solution (34 mL) was dropwise added over aperiod of 30 minutes. The dropwise adding operation was carried outunder cooling with ice so that the internal temperature would not exceed10° C. After stirring at room temperature for two hours, water anddiethyl ether were added for liquid separation, and the organic layerwas recovered. The recovered organic layer was washed with a saturatedsodium carbonate aqueous solution and dried by an addition of anhydrousmagnesium sulfate. By filtration under reduced pressure, anhydrousmagnesium sulfate was removed, and the filtrate was concentrated toobtain powdery crystal. Recrystallization was carried out by using asolvent mixture (90 mL) of dichloromethane and hexane, to obtaincompound (R-1) (8.93 g). The yield was 94%.

Preparation Example for Compound (2Bb1-1)

Into a 500 mL four-necked flask equipped with a reflux condenser, astirrer and a dropping apparatus, compound (R-1) (8.0 g, 0.027 mol)obtained in the above Preparation Example, triethylamine (3.40 g, 0.033mol) and tetrahydrofuran (300 mL) were added. In a nitrogen stream,acrylic acid chloride (2.94 g, 0.033 mol) was dropwise added undercooling with ice so that the internal temperature would not exceed 20°C. After stirring 24 hours, a mixture comprising concentratedhydrochloric acid (2 mL), ice (20 g) and water (30 mL) was added forliquid separation, and an organic layer was recovered. The recoveredorganic layer was washed with water, and then, the organic layer wasdried over anhydrous magnesium sulfate. After filtrating off anhydrousmagnesium sulfate, the solvent was distilled off to obtain compound(2Bb1-1) (8.1 g). The yield was 86%.

The phase transition temperature from the crystal phase to the nematicphase of compound (2Bb1-1) was 160° C., and the phase transitiontemperature from the nematic phase to the isotropic phase was 198° C.(extrapolation value). Further, Δn of compound (2Bb1-1) against a laserbeam having a wavelength of 589 nm at 50° C. was 0.18 (extrapolationvalue).

The ¹HNMR spectrum of compound (2Bb1-1) is shown below.

¹HNMR (400 MHz, solvent: CDCl₃, internal standard: TMS) δ (ppm): 0.91(t, 3H), 1.09 (m, 2H), 1.1-1.4 (m, 5H), 1.50 (m, 2H), 1.91 (t, 4H), 2.51(m, 1H), 5.9-6.7 (m, 3H), 7.0-7.3 (dd, 4H), 7.4-7.6 (dd, 4H)

(3) Preparation and Evaluation Example for Liquid Crystal Element (3-1)Preparation of Liquid Cyrstal Element

Each liquid crystal composition obtained in (2) was injected into a cellobtained in (1) at 90° C. in the case of the composition usingpolymerizable liquid crystal 1 or 2. Photopolymerization was conductedunder irradiation with ultraviolet light with an intensity of 45 mW/cm²at 66° C. so that the total amount of light became 8,100 mJ/cm² toobtain a liquid crystal element.

Further, the composition using polymerizable liquid crystal 3 wasinjected at 120° C., and photopolymerization was conducted underirradiation with ultraviolet light with an intensity of 45 mW/cm² at120° C. so that the total amount of light became 8,100 mJ/cm² to obtaina liquid crystal element.

Further, the composition using polymerizable liquid crystal 4 wasinjected at 100° C., and photopolymerization was conducted underirradiation with ultraviolet light with an intensity of 45 mW/cm² at 50°C. so that the total amount of light became 8,100 mJ/cm² to obtain aliquid crystal element.

(3-2) Evaluation of Liquid Crystal Element

Each liquid crystal element obtained in (3-1) was irradiated with a Krlaser (multimode at wavelengths of 407 nm and 413 nm) by means of a Krlaser apparatus (tradename: Innova 302, manufactured by Coherent, Inc.)to carry out an accelerated exposure test with blue laser beam. The testtemperature was 80° C., and the total energy was 30 Wh/mm² with respectto the liquid crystal elements using polymerizable liquid crystal 1 andpolymerizable liquid crystal 2, 40 Wh/mm² with respect to the liquidcrystal element using polymerizable liquid crystal 3, and 35 Wh/mm² withrespect to the liquid crystal element using polymerizable liquid crystal4.

In the respective Examples, the changes in transmittance between beforeand after the accelerated exposure test, are shown in Tables 1 to 4.Here, a case where the transmittance after the test became smaller thanthe transmittance before the test, is shown by a minus value.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Polymerizable liquid crystal 1 1 1 1Polymerization initiator IC754 0.5 0.5 0.5 0.5 Polymerization inhibitor2NDP 0.2 0.2 — — Hindered phenol compound Compound (B-1) — — — 0.2Compound (B-4) — — — — Hindered amine compound Compound (A2-3) — 0.3 0.3— Compound (A3-1) — — — — Δn of polymer liquid crystal 0.0437 0.0420 —0.0411 composition Total energy in exposure test (Wh/mm²) 30 30 — 30Change in transmittance (%) −0.8 −1.3 — −0.8

TABLE 2 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Polymerizable liquid crystal 1 1 2 2Polymerization initiator IC754 0.5 0.5 0.5 0.5 Polymerization inhibitor2NDP — — — — Hindered phenol compound Compound (B-1) 0.2 0.2 0.2 0.2Compound (B-4) — — — — Hindered amine compound Compound (A2-3) 0.3 — —0.3 Compound (A3-1) — 0.3 — — Δn of polymer liquid crystal 0.0412 0.04000.0410 0.0405 composition Total energy in exposure test (Wh/mm²) 30 3030 30 Change in transmittance (%) 0.0 −0.1 −0.9 0.0

TABLE 3 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Polymerizable liquid crystal 3 3 3 3Polymerization initiator IC754 0.5 0.5 0.5 0.5 Polymerization inhibitor2NDP 1.5 — — — Hindered phenol compound Compound (B-1) — — — — Compound(B-4) — — 1.5 1.5 Hindered amine compound Compound (A2-3) — 0.3 — 0.3Compound (A3-1) — — — — Δn of polymer liquid crystal 0.0387 — 0.03530.0360 composition Total energy in exposure test (Wh/mm²) 40 — 40 40Change in transmittance (%) −2.5 — −6.9 0.3

TABLE 4 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Polymerizable liquid crystal 3 4 4 4Polymerization initiator IC754 0.5 0.5 0.5 0.5 Polymerization inhibitor2NDP — — — — Hindered phenol compound Compound (B-1) — — 0.2 0.2Compound (B-4) 1.5 — — — Hindered amine compound Compound (A2-3) — 0.3 —0.3 Compound (A3-1) 0.3 — — — Δn of polymer liquid crystal 0.0357 —0.1532 0.1531 composition Total energy in exposure test (Wh/mm²) 40 — 3535 Change in transmittance (%) −0.1 — −1.7 0.0

From these results, it has been found possible to suppress the change intransmittance between before and after the test, by using a hinderedamine compound and a hindered phenol compound.

In Examples 3 and 14, no polymerization inhibitor was added, wherebynon-uniformity in the injection of the polymerizable liquid crystalcomposition into the cell, resulted, and the in-plane distribution ofthe retardation value became remarkably large. Further, in Example 10,no polymerization inhibitor was added, whereby at the time of theinjection into the cell, the polymerizable liquid crystal compositionunderwent thermal polymerization.

INDUSTRIAL APPLICABILITY

The liquid crystal optical modulation element of the present inventionis capable of maintaining good optical modulation characteristics over along period of time and is therefore useful as an optical modulationelement to modulate a blue laser beam, and it can be utilized as apolarization conversion element, a light quantity-controlling element,an aberration-correcting element or a diffraction element and can beused for an optical head device or a projector.

The entire disclosure of Japanese Patent Application No. 2005-302812filed on Oct. 18, 2005 including specification, claims and summary isincorporated herein by reference in its entirety.

1. A liquid crystal optical modulation element to modulate a laser beamhaving a wavelength of at most 500 nm, which comprises a layer of apolymer liquid crystal composition sandwiched between a pair oftransparent substrates facing each other, characterized in that each ofthe pair of transparent substrates has an alignment film on the surfacewhich faces the other transparent substrate, and the polymer liquidcrystal composition is a polymer liquid crystal containing a hinderedamine compound and a hindered phenol compound.
 2. The liquid crystaloptical modulation element according to claim 1, wherein the polymerliquid crystal composition is one obtainable by polymerizing apolymerizable liquid crystal composition comprising a polymerizableliquid crystal, a hindered amine compound and a hindered phenolcompound.
 3. The liquid crystal optical modulation element according toclaim 2, wherein the content of the hindered amine compound is from 0.05to 5 mass % based on the polymerizable liquid crystal.
 4. The liquidcrystal optical modulation element according to claim 2, wherein thecontent of the hindered phenol compound is from 0.05 to 10 mass % basedon the polymerizable liquid crystal.
 5. The liquid crystal opticalmodulation element according to claim 2, wherein the polymerizableliquid crystal contains at least one of the following compounds (2) and(3):CH₂═CR¹—COO-(L¹)_(k1)-E¹-E²-E³-(E⁴)_(m)-(E⁵)_(n)-R²   (2)CH₂═CR³—COO-(L²)_(k2)-G¹-G²-G³-G⁴-R⁴   (3) wherein each of R¹ and R³ isa hydrogen atom or a methyl group; R² is a C₁₋₈ alkyl group; R⁴ is aC₁₋₈ alkyl group or a fluorine atom; L¹ is —(CH₂)_(p1)O—, —(CH₂)_(q1)—,-Cy-COO—, -Cy-OCO—, -E⁶-(CH₂)₂—, -E⁷-CH₂O— or -E⁸-O— (wherein Cy is atrans-1,4-cyclohexylene group, each of p1 and q1 which are independentof each other, is an integer of from 2 to 8); L² is —(CH₂)_(p2)O— or—(CH₂)_(q2)— (wherein each of p2 and q2 which are independent of eachother, is an integer of from 2 to 8); each of E¹, E², E³, E⁴, E⁵, E⁶, E⁷and E⁸ which are independent of one another, is a 1,4-phenylene group ora trans-1,4-cyclohexylene group (provided that at least one of E¹, E²and E³ is a trans-1,4-cyclohexylene group, and in a case where L¹ is-Cy-OCO—, E¹ is a trans-1,4-cyclohexylene group); G¹ is a 1,4-phenylenegroup, each of G², G³ and G⁴ which are independent of one another is a1,4-phenylene group or a trans-1,4-cyclohexylene group, and at least oneof G² and G³ is a trans-1,4-cyclohexylene group (provided that the1,4-phenylene group and trans-1,4-cyclohexylene group in G¹ to G⁴ may besuch that a hydrogen atom bonded to a carbon atom in each group may besubstituted by a fluorine atom, a chlorine atom or a methyl group); andeach of k1, k2, m and n which are independent of one another, is 0 or 1,provided that when k1 is 1 and L¹ is -Cy-COO—, -Cy-OCO—, -E⁶-(CH₂)₂—,-E⁷-CH₂O— or -E⁸-O—, at least one of m and n is
 0. 6. The liquid crystaloptical modulation element according to claim 1, which is used for alaser beam having a wavelength of from 300 to 450 nm.
 7. An optical headdevice comprising a light source for emitting a laser beam having awavelength of at most 500 nm, an objective lens for converging the laserbeam emitted from the light source on an optical recording medium, aphotodetector for receiving the light converged and reflected on theoptical recording medium, and the liquid crystal optical modulationelement as defined in claim 1, disposed in an optical path between thelight source and the optical recording medium or in an optical pathbetween the optical recording medium and the photodetector.